The present invention relates to a cell receiving apparatus and traffic control system suitable, for example, for control of available-bit-rate traffic in a communication network employing the asynchronous transfer mode.
The asynchronous transfer mode (ATM) provides various service categories, so that the user can select the type of service best suited for the type of data to be transmitted (audio data, video data, various other types of data, or a mixture thereof). Available bit rate (ABR) is one of the service categories. In ABR service, a minimum cell rate and a peak cell rate are established for a connection, and the network tries to provide the best quality of service for as much traffic as it can handle within these limits. ABR service is managed by the use of resource management (RM) cells, which are sent between the source and destination nodes (including virtual source and virtual destination nodes) in the connection. Traffic management enables ABR connections to be kept operating despite cell traffic fluctuations and variations in the availability of bandwidth and other network resources.
Incidentally, an ATM cell is a fixed-length data packet, so cell rate is synonymous with bandwidth.
Various methods of ABR traffic management by ATM switches have been proposed. One of the main methods specifies an explicit cell rate (ECR) in the RM cells, and is known as ECR marking. The terms explicit rate (ER) and ER marking are also used, but the acronym ECR will be employed herein.
In the conventional ECR marking system, when a source node sends cells to a destination node through an ATM switch, the source node periodically inserts RM cells in the cellstream, specifying a desired cell rate in the ECR field. The ATM switch, operating as a virtual destination (VD), receives the RM cells, modifies various information in them, and returns them to the source node. One of the modified values may be the ECR value, which the switch reduces if the desired rate is too high to allow. The source node updates its allowable cell rate according to the ECR value specified by the switch.
A similar control scheme is employed on the path between the ATM switch and the destination node, the ATM switch acting as a virtual source (VS).
The problem in ECR marking is how the ATM switch should calculate the ECR value for each connection. Needless to say, the calculation must take account of the current cell rates of other connections sharing the same path or the same ATM switch resources. ATM standards organizations have not recommended a generic algorithm for ECR calculation. Several algorithms have been proposed, but the proposed algorithms leave room for improvement in regard to fairness and adaptability to changing communication conditions.